1. Field of the Invention
The present invention relates to a shock absorber and a method for producing the same, and more specifically to a shock absorber comprising a cushion structure of three-dimensional spring construction having a large void comprising a random loop formed by hot extruding a polyester elastomer, a nylon elastomer, an urethane elastomer or an olefin elastomer comprising a high-molecular material having both properties of thermoplastic resin or rubber and engineering plastics, for instance, a polyester thermoplastic elastomer to form a continuous strip, and curling or looping said strip while it is in a molten state to bring, for instance, adjoining strip sections in interlocking contact with each other. The cushion structure, which can reduce plastic deformation of strip bends portion caused by compression deformation, and which has a restoring property that enables the cushion structure to be restored by a recovery force of strip rubber elasticity immediately upon a release of stress, is embedded in a foamed and hardened filler. The present invention also relates to a shock absorber production method as well as a filler suitable for use with the shock absorber.
2. Description of the Related Art
A shock absorber material has been provided in the form of a so-called cushion drum as an example. This cushion drum is used for the purpose of absorbing shocks generated upon collision of vehicles with barriers or other facilities positioned at turning points on highways, thereby reducing damages to both the human body and the facilities, and is built up of a drum member with a 100 to 400-liter water bag contained therein.
Another version of the shock absorber positioned on highways, etc. is a bellows type fender made up of steel.
The U.S. Department of Transportation xe2x80x9cSafety Standard for Securing Driversxe2x80x9d prescribing the safety standard for drivers states that when gravitational acceleration (gravity on the floor of a vehicle in the back-and-forth direction) applied to a vehicle upon collision is less than 20 G, damage to passengers can be reduced to a vitally safe level (at which hospital care is required, leaving serious traumas. At 15 G or less, the damage can be reduced to a level free of any trauma (at which hospital care is required). At 12 G or less, the damage can be reduced to a level at which clinical care is needed but hospital care is not always needed.
Even with the aforesaid cushion drum, for instance, a 900xc3x97900xc3x97900 mm drum having a weight of 18 kg and a 400 liter water bag, a 1.5 ton automobile traveling at 65 km/h can be reduced to 45.7 km/h upon collision.
Upon receipt of impact energy, however, the aforesaid cushion drum is deformed, broken off, and completely scattered away. When a traveling car, etc. collides with this shock absorber, it is thus impossible to absorb the resulting shocks completely. Consequently, the car unavoidably collides with a barrier located behind the shock absorber.
The aforesaid cushion drum is made up of a drum member with a water bag contained therein, as already mentioned. Thus, this cushion drum itself is formed into a desired shape to construct, for instance, a base of signposting, a wall to be positioned at a curve, or a separator or the like to be positioned at a turning point.
Instead of water, other substance may be filled in a cushion drum such as the aforesaid one. However, such a shock absorber is usually positioned outdoors, for instance, on roads, and so is required to have a weight heavy-enough to be unsusceptible to displacement due to winds, vibrations, and mischief, ultraviolet shielding capabilities that can prevent degradation due to exposure to ultraviolet radiation, and given endurance that can dispense with maintenance. In addition, the shock absorber is required to have given strength that allows the shock absorber per se to absorb shocks.
When the aforesaid cushion drum member is filled with known concrete or the like, conditions regarding weight, flame retardance, endurance, etc. may be satisfied. However, gravitational acceleration upon collision cannot be brought down to the aforesaid vitally safe level of 20 G or lower because the filled concrete has an increased strength.
On the other hand, the aforesaid bellows type of shock absorbing fender made up of steel is designed to absorb shocks applied to a vehicle upon collision. Given the fact that an accident-prone vehicle having a engine displacement of 2,000 cc or greater has a weight of about 1.8 tons, however, this fender cannot stand up to collision of the vehicle therewith. In addition, the bellows form of shock absorbing fender takes much cost, time, and trouble to install.
In view of the aforesaid problems associated with the prior art, it is an object of the invention to provide a shock absorber which has high shock absorption capabilities. Especially when a vehicle collides with the shock absorber, gravitational acceleration (gravity applied on the floor of the vehicle in the back-and-forth direction) applied on the vehicle can be brought down to 20 G or less, preferably 15 G or less, and more preferably 12 G or less. In addition, the shock absorber of the invention is well capable of absorbing shocks, because it comprises as a part of shock absorber a filler that can absorb shocks upon collision of a vehicle or the like therewith, and makes it easy to achieve any desired impact resistance depending on the object to be protected. Further, the shock absorber can be easily produced with shape depending on purpose. Another object of the invention is to provide a method for producing such a shock absorber. Yet another object of the invention is to provide a filler suitable for use with the shock absorber of the invention.
A further object of the invention is to provide a shock absorber filler which has a breaking strength enough to enable a shock absorber to be broken upon receipt of a certain or larger shock, thereby absorbing the shock while it satisfies conditions regarding the necessary weight, flame retardance, weather resistance, endurance, etc.
To achieve the aforesaid objects, the present invention provides a shock absorber comprising a cushion structure of three-dimensional spring construction, which has a large void provided by a random curl or loop formed by hot extruding, a thermoplastic resin to form a continuous strip and curling or looping said strip in a molten state to bring adjoining strip sections into interlocking contact with each other. Hereinafter, this cushion structure will simply be referred to as the xe2x80x9ccushion structurexe2x80x9d. In the invention, the cushion structure may be obtained by putting a plurality of cushion structure members, each having high cushion performance and buckling resistance and a certain thickness, one upon another parallel in a thickness direction or rolling up one side of a cushion member with a given thickness. Then, the cushion structure is embedded in a foamed and hardened filler containing a hydratable, hydraulic binder while a part of the cushion structure is exposed on an shock-receiving surface.
Preferably, the cushion structure should have a bulk specific gravity of 0.003 to 0.3 g/cm3. At less than the lower limit value, the effect on shock absorption becomes slender, and at greater than the upper limit value, the amount of the binder mixed with water and a foaming agent to penetrate through the cushion structure becomes small, resulting in poor impact resistance.
Preferably, the cushion structure should have a strip diameter of 0.1 mm to 3 mm although depending on the type and bulk density of the thermoplastic resin. In view of shock absorption capabilities, the thus constructed cushion structure should also have a specific gravity of 0.2 to 1.3. The cushion structure may be constructed by stacking a plurality of cushion structure members varying in bulk specific gravity or strip diameter one upon another in the thickness direction.
The present invention also provide a shock absorber production method, characterized by placing a cushion structure of three-dimensional spring construction in a mold, and pouring and aging a foaming filler containing a hydratable, hydraulic binder in said mold, said cushion structure having a large void provided by a random curl or loop formed by hot extruding a thermoplastic resin to form a continuous strip and curling or looping said strip in a molten state to bring adjacent strip sections into interlocking contact with each other. Preferably, the mold should be a plastic film or sheet container which per se forms an outer face or wall of a shock absorber. In the invention, however, it is acceptable to use other plastic molding containers.
Regarding the strength of the shock absorber according to the invention, it may be possible to make the rigidity of the shock absorber lower than that of the member to collide therewith, e.g., a vehicle, thereby absorbing all collision energy into the shock absorber. In this case, however, it is required to make the shock absorber longer and heavier than contemplated in the invention. Alternatively, it may be possible to make the rigidity of the shock absorber higher than that of the member to collide therewith, e.g., a vehicle, thereby absorbing shocks upon receipt of a shock exceeding the rigidity of the vehicle. In this case, however, gravitational acceleration (gravity applied on the floor of the vehicle in the back-and-forth direction) applied on the vehicle upon collision with the shock absorber is of the order of 30 G, and so damage to passengers cannot be reduced to the vitally safe level. It is thus preferable that the shock absorber of the invention has a strength on the same level as the rigidity of the vehicle, so that the shock absorber can absorb impact energy in an integral fashion with the vehicle.
To allow the shock absorber to have such strength, the filler for the shock absorber according to the invention should be formed by kneading together 4.0 to 33.3 wt % of a hydratable, hydraulic binder, 2.7 to 46.7 wt % of calcium carbonate (stone dust), 2.7 to 53.3 wt % of an aggregate (sand), 13.3 to 53.3 wt % of water, and 1.4 to 10.0 wt % of a foaming agent (including diluting water).
The filler should have a breaking load of 10 kgf/cm2 or less, preferably 4 kgf/cm2 or less, and more preferably 2 kgf/cm2 or less, as found after dried and hardened.
The hydratable, hydraulic binder contained in the filler may comprise lime aluminate and lime silicate in chemical combining components. More specifically, the binder of the invention may comprises 15 to 18% of 3CaOAl2O3 as the lime aluminate and 55 to 60% of 3CaOSiO2 and 10 to 20% of 2CaOSiO2 as the lime silicate.